package com.leetcode.middle;

import org.junit.Test;

public class LongestPalindrome {
	
	@Test
	/**
	 * 给定一个字符串 s，找到 s 中最长的回文子串。你可以假设 s 的最大长度为 1000。
示例 1：
输入: "babad"
输出: "bab"
注意: "aba" 也是一个有效答案。
	 */
	public void test() {
		String str = "asddfbabbabadsdf";
		System.out.println(longestPalindrome(str));
	}
	public String longestPalindrome(String s) {
	    if (s == null || s.length() < 1) return "";
	    int start = 0, end = 0;
	    for (int i = 0; i < s.length(); i++) {
	        int len1 = expandAroundCenter(s, i, i);
	        int len2 = expandAroundCenter(s, i, i + 1);
	        int len = Math.max(len1, len2);
	        if (len > end - start) {
	            start = i - (len - 1) / 2;
	            end = i + len / 2;
	        }
	    }
	    return s.substring(start, end + 1);
	}

	private int expandAroundCenter(String s, int left, int right) {
	    int L = left, R = right;
	    while (L >= 0 && R < s.length() && s.charAt(L) == s.charAt(R)) {
	        L--;
	        R++;
	    }
	    return R - L - 1;
	}

}
